Absorption refrigeration system of the inert gas type



1954 s. M. BACKSTROM 2,664,717

ABSORPTION REFRIGERATION SYSTEM OF THE INERT GAS TYPE Filed April 22, 1950 1' zw iwm I W [M Patented Jan. 5, 1954 ABSORPTION REFRIGERATION SYSTEM OF V THE INERT GAS TYPE Sigurd Mattias Backstrom, Stockholm, Sweden, assignorto AktiebolagetElektrolux, Stockholm,

Sweden, a corporation of Sweden Application April 22, 1950, Serial No. 157,586 Claims priority, application Sweden May 5, 1949 My invention relates to refrigeration, and more particularly to a refrigeration system employing evaporation of refrigerant fluid in the presence of inert gas which is circulated by a force produced or developed within :the system. Such motivating force for causing circulation of inert gas is produced by the difference in specific weight of columns of inert gas rich and weak in refrigerant, respectively, in the inert gas circuit.

It is an object of the invention to improve the operation of systems of this type having low and higher temperature evaporator sections or cooling elements, particularly to effect an extremely low temperature in the low temperature evaporator section.

Another object of'the invention is to provide an improvement in such a system having low and higher-temperatureevaporator sections .in which the circulation of inert gas isbetter correlated to the temperature level at which the low temperature evaporator section operates.

A furtherobject is to provide an improvement in such a system having a low temperature evaporator section suitable for freezing. purposes in which the force developed within the system for causing circulation of inert gas through the low. temperature evaporator section. is x more nearly related to the specific weight of the inert gas in such evaporator section rather than to the specific weight of: inert gassinf other parts of the system, having a higher partial-pressure of refrigerant.

A still further object is'to provide an improve: ment in such a system having low andhigher temperature evaporator sections by correlating the circulation of inert'gas through the -low-tem--. perature section to the temperature level at which evaporation of refrigerant. is effected therein, and by subdividing the inert gas into a plurality of streams in parallel relation not only in the low temperature evaporator'section but desirably also inthe'absorber to insure such gas circulation at a reduced flow rate through the low temperature evaporator section.

The invention, together with theabove and further objects and advantages thereof, willbei. more fully understood upon referenceto'the fOI-Z. lowing description and accompanying drawing forming a part of this specification, and of whichthe single figure illustrates more-or less diagram-. matically a refrigeration system embodyingthe invention.

Referring to the'drawing, I have "shownmy* 9 Claims. (01. 62-1195) ample. The heating tube ll may be heated in any suitable manner, as by an electrical heating element disposed within the lower part of the heating tube or by a liquid or gaseous fuel burner M which is adapted to project its flame into the lower end of the tube.

. The heat supplied to the boiler l0 and its contents expels refrigerant vapor out of solution, and such vapor passes upwardly through a conduit I5 andair cooled rectifier l6 into an air cooled condenser I! in which it is condensed and liquefied. Liquid refrigerant flows from condenser)" through a conduit l8,vessel l9 and conduit 20 into a first evaporator section 2|. As. will be explained more fully hereinafter, liquid refrigerantin the evaporator section 2|- evaporates and, diffuses into an inert pressure equalizing gas, such as hydrogen, which enters through a conduit-22. ,Due to evaporation of refrigerant into inert gas, a refrigerating effect is producedwith consequent absorption of heat from the, surroundings. q

.:.Inert gas enriched" in refrigerant vapor and formedjin" evaporator section 2 flows therefrom through. a conduit 23 and onewpassage 24'of a gas heat exchanger 25 to an absorber 26 having an absorber vessel 21 at the lower part thereof. As will beexplained more fully hereinafter, the gas mixture in absorber 2B flows counter-current to downwardly flowing absorption liquid which enters through a conduit 28. The absorption liquid absorbs refrigerant vapor from inert gas, and inert gas weak in refrigerant vapor flows from absorber 26 in a path of flow including a passage 29 of gas heat exchanger 25 and conduit 22 into evaporator section 2|.

Absorption solution enriched in refrigerant flows from the absorber 25 into absorber vessel 21 and from 'thelatter through a conduit 30 and an inner passage or pipe 3| of a liquid heat exchanger 32 into the lower end of a vapor lift tube or pipe 33. Liquid is raised by vapor-liquid lift actionthrough pipe 33, which is in thermal relationwith the heating tube II at 34, into the upper part of the boiler I0. Refrigerant vapor invention in connection with an absorption're expelled. out of solution in boiler. I0, together with refrigerant vapor entering through pipe 33, flows upwardly through conduit 55 to the condenser H, as previously explained. The abs-orption liquid from which refrigerant vapor has been expelled flows from the boiler through a connection '35, outer passage 36 of liquid heat exchanger 32 and conduit 31 whose upper end is in communication with the conduit 28, as will be explained presently. The circulation of absorption solution in the liquid circuit just described is eifected by raising of liquid through pipe 33.

The outlet end of condenser .fl connected by conduit 58, vessel 59 and conduit 60 to apart of the gas circuit, as at 6|, for example, so that any inert gas which may pass through thecondensercan flow into the gas circuit. Refrigerant vapor not liquefied in the condenser 11 flows through conduit 58 to displace inert gas in vessel59 and force such gas into the gas circuit. The effect of forcing'gas into .thegas circuitin this manner is'to raise the total pressure in the entire system whereby an adequate condensing'pressure is obtained to insure condensation of refrigerant vapor in condenser 11.

In order to effect a low refrigerating temperature in evaporator section 2! the vessel I9 is arranged to operate as a precooler for reducing the temperature of liquid refrigerant supplied to evaporator section 2!. In vessel I9 liquid refrigerant conducted therethrough is precooled-by evaporation of refrigerant into inert gas partially enriched in refrigerant and flowing thereto through a conduit 38 which is connected to an upper part of evaporator section 2|. Liquid refrigerant in vessel 1 9, which may be referredto as a second evaporator section, evaporates and diffuses into partially enriched gas, thereby taking up heat from the liquid refrigerant. Liquid 're-' frigerant precooled in this manner passes to the upper part of evaporator section 2! through conduit which is formed to provide a liquid trap.

A third evaporator section 39 provided with heat transfer fins 4flis connectedto receive inert gas'and liquid refrigerant from a lower part of evaporator section 2|. Inert gas enriched in refrigerant flows from evaporator section 39 through a conduit M to whichis also connected a conduit'42 whose upper end-is connected to vessel l9. Hence, enriched inert gas flows-from both the precooler vessel or second evaporator section I9 and the third evaporator section 39 through conduit M to an outerpassage 430i a second gas heat exchanger i l and thence'through a conduit &5 to the absorber vessel'fl.

The circulation of inert gas in refrigeration systemsof the type under consideration is dueto the difference in specific weight of the columns of gas 'enriched and weak, respectivelyin refrigerant vapor. Since acolumn of'gas'enriched'in refrigerant vapor and flowing from an evaporator to the absorber is heavier than a *eolumnof gas weak in refrigerantvaporand flowing from the absorber to the .evaporator,=a force is pro-, duced or developed within the system'for causing circulation of gas.

In refrigeration-systems of. the inert gas :type it is usually the practice to provideseveral evaporator sections, one or which serves as aifreezing section adapted to operate belowthe freezing temperature of water and another of Whichis :employed for general food-preservation and isadapted to operate above vsuchlfreezing temperature. The-low and higher temperature evaporator sections are usually connected in series and the inert as flows successively through the freezing and higher temperature evaporator sections, so that the gas in the higher temperature sections contains agreateramountof refrigerantv-apor than the gas in the freezing section. Since the driving force developed for causing circulation of inert gas is dependent upon the increase in specific weight or density of inert gas due to evaporation of refrigerant in both evaporator sections, the

driving force for effecting gas circulation generally is determined by inert gas having the highestpartial pressure of refrigerant and therefore, the highest-evaporating temperature of refrigerant in the system.

"It is already known that the circulation of I inert gas should not be greater than necessary to take care of the quantity of refrigerant that evaporates to satisfy and meet the load or refrigerating requirement. When the circulation of gas is igreaterithaninecessary, the .iefliciency of the gas "heat exchanger is reduced and so-called fgas.lossestresult due to thefact that a greater quantity of weak'inert gas from the relatively high temperature absorber is introduced into the freezing-evaporator section than is actually required. Hence, while this probelm has been recognized and provisionhas been made to effect a reduction :in circulation of inert gas under certain operating conditions, such reduction in gas circulation has been effected in both the freezing and higher temperature evaporator sections and is dependent uponfiow-of unevaporated refrigerant from both the low and higher temperature evaporator sections.

In accordance with my invention the inert gas circuit including the low temperature evaporator section 2| andabsorber-ZS is formed and arranged so that the circulation of inert gas through such low temperature evaporator section is correlated-more eifectively to the freezing temperatures produced by this evaporator sectionand-not dependent to any substantial extent upon inert gas having the highest partial pressure of refrigerant in the system. In the preferredembodiment of the invention illustrated, this is accomplished by providing in the low temperature evaporator section 2! and also inthe absorber .Z'G'a'number of paths of flow for inert'gas whichare connected in parallel.

The low temperature evaporator section 2! comprises apair of spaced apart headers 46 and 41 between which are connected a number of inclined conduits 48-.disposed at different levels. The-conduits 48 arein open communication with the headers 46 and '41, the lower ends of the top andintermediateconduits being formed with liquid barriers 49- to divertliquid into conduits 56 whose lower ends are connected to the higher lo cated-end of the next lower conduit 48. Hence. liquid will flow from vessel [9 into the top ccn duit through theconduitl20. From the lower end of :the top conduit "48 liquid passes through the first connection 50' into the'upper end of the intermediate conduitlland from the lower end of the latter through the second connection 5-3 intothe bottom conduit 48. The bottom conduit 48 maysalso be provided-with a liquid barrier 49 from which'liquid will pass into the bottom of header and then flow by gravity through the evaporator section .39.

The conduits 48 maybe provided with internal screening, or the inner surfaces be otherwise formed .to effect distribution of refrigerantby capillary action, for example, so

that an extensive gas and liquid contact surface will be obtained. Inert gas weak in refrigerant flows from conduit 22 into header 46 where the gas is subdivided into a plurality of streams for flow through the several'conduits 48. The streams of gas merge in header 4'! and flow through conduit 23 to the absorber 26, as previously explained.

The absorber 26 also comprises a pair of spaced apart headers 5| and 52 between which are connected a'number of inclined conduits 53. The lower ends of conduits 53 are formed with liquid barriers 54 and liquid is conducted from the lower ends of the top and intermediate conduits 53 through connections 55 to the next lower conduit.

It will now be apparent that absorption liquid entering the top conduit 53 through conduit 28 flows downwardly through each conduit 53 and passes from the lower end of bottom conduit 53 into the absorber vessel 21. Inert gas enriched in refrigerant flows from conduit 23 through the passage 24 of gas heat exchanger 25 into the absorber header 5|. The inert gas is then subdivided into several streams for fiow through the conduits 53 in which refrigerant vapor is absorbed into solution. Inert gas weak in refrigerant fiows upwardly through header 52 whose upper end is in communication with the passage 29 of the gas heat exchanger.

Since inertgas weak in refrigerant and flowing from absorber 28 is initially introduced into the first evaporator section 2|, and precooled liquid refrigerant evaporates and diffuses into such weak gas with consequent absorption of heat from the surroundings, a low temperature refrigerating efiect is produced which is suitable for freezing purposes. By reason of the low-tem- 'perature at which the first evaporator section 2| operates, the partial vapor pressure of refrigerant in the inert gas emerging from header 4'! and flowing to the absorber 26 is comparatively low. Due to absorption of refrigerant into absorption solution in the absorber 26, inert gas weak in refrigerant flows upwardly in absorber header 52 and flows through an inner passage 56 of the second gas heat exchanger 44.

Absorption liquid weak in refrigerant and flowing from boiler I0 is initially introduced into the presence of inert gas in the inner passage 55 of the gas heat exchanger 44. The lower end of passage 56 is formed with a barrier or dam 51 for diverting absorption liquid into conduit 23 for flow through successive conduits 53 of the absorber 26. It will therefore be evident that the weak absorption liquid flowing from the boiler it i is not only cooled in the liquid heat exchanger 36 but also cooled further by flowing in heat exchange relation with relatively cool gas in the gas heat exchanger 44, such cool gas flowing to the outer passage 43 of the latter from the second and third evaporator sections I9 and 39, re-

spectively.

Since the part of the absorber-at which th weak absorption liquid is introducedand the weak inert gas passes or emerges therefrom tends to operate at a higher temperature than the rest of the absorber, it is advantageous to shift such part from the absorber 26 proper to the second gas heat exchanger 44; In this manner-the intense cooling eflect of the cool enriched inert gas in the outer passage 43 of heat exchanger 44 effectively takes up heat from both the weak absorption liquid and weak inert gas, and, asa resultof such increased cooling, the inert gas :passing out of contact with absorption liquid and flowing tothe 6 first evaporator section 2| will be deprived of as much refrigerant as possible.

Inert gas enriched in refrigerant fiows from the outer passage 43 of gas heat exchanger 44 through conduit 45 into the end of absorber vessel 21 opposite to that at which'the header 5| is connected to the absorber vessel. Since the gas mixture flowing through conduit 45 is gas which is enriched in refrigerant in the vessel l9 and second evaporator 39, such gas has the highest partial pressure of refrigerant in the system. However, such rich gas passes through the absorber vessel 21 before entering the lower end of the header 5|, and in passing in intimate contact with absorption liquid in the vessel 21 the liquid absorbs refrigerant vapor from the inert gas.

Hence, the absorber vessel 21 serves as an active part of the absorber unit of the system, and the partial vapor pressure of refrigerant in the inert gas passing through the vessel is reduced by the time it enters the lower end of absorber header 5| and mixes with inert gas flowing thereto from the low temperature evaporator section 2|. While absorption of refrigerant into solution may take place at a relatively high temperature in the absorber vessel 21, such absorption of refrigerant is realized because of the comparatively high partial pressure of refrigerant vapor in the gas mixture.

It will now be understood that the circulation of inert gas between the low temperature evaporator section 2| and absorber 26 is primarily due to the difference in specific weight of the column of weak gas flowing from the absorber 25 to evaporator section 2! and the column of enriched gas flowing from evaporator section 2 to the absorber 25. Accordingly, the force developed within the system for causing circulation of inert gas through the low temperature evaporator section 2| will be more nearly related to and better correlated with the specific weight of the gas mixture produced in the low temperature evaporator section rather than to the higher specific weight of the inert gas flowing from the other evaporator sections through conduit 45 into the absorber vessel 21. Even though there sometimes may be a tendency for the gas mixture from absorber vessel 21 to remain seg regated in header 5| from the gas mixture of less specific weight entering the upper part of such absorber header, and the heavier gas mixture may tend to fiow through the lower located conduits 53 and the lighter gas mixture through the higher located conduits, nevertheless the gas circulation will be better correlated to the temperature level at which the low temperature evaporator section 2| operates. This is, so because the driving force developed in the gas circuit by the evaporationof refrigerant in the evaporator section 2| is less than the sum total of the driving forces developed in all of. the

places of evaporation in the system.

peratures of 5f C ar id lower. With such an arrangementythe resistance oiferedto how of inert gas is reduced to such an extent that adequate gas circulation is assured under all operating conditions encountered in practice even though the driving or motivating force to cause such gas circulation is not of the highest magnitude capable of being developed in the system, as is the case when advantage is taken of inert gas having :the highest partial pressure of refrigerant vapor which is produced in one or more higher temperature evaporator sections.

While I have shown and described a single embodiment of my invention, it will be apparent to those skilled in the art that modifications and changes may be made without departing from the spirit and scope of the invention. I therefore do not wish to be limited to the embodiment shown in the drawing and described in the specification, and I intend in the following claims to cover all modifications .and changes which fall within the true spirit and scope of the invention.

What-is claimed is:

1. In absorption refrigeration apparatus, a circuit for circulation of inert gas including evaporating means in which liquid refrigerant evaporates in the presence of inert gas to produce a refrigeratingeffect and absorbing means in which refrigerant vaporis absorbed frominert gas into absorption liquid, at least one of said means comprising a pair of spaced apart vertically extending end headers, a number of horizontally extending conduits at different levels, each of said conduits having one end connected to one end header and the opposite end connected .to the other end header, means for conducting liquid for said one .means to the uppermost conduit, and connections for conducting liquid through successively lower conduits for gravity flow therein, the circulation of inert gas through said conduits in a number of parallel flow paths fromone headerto the other header being effected solely due to the varying partial pressure of refrigerant Vapor in different parts of theinert gas circuit.

2. In absorption refrigeration apparatus, a circuit for circulation of inert gas including evaporating .means in which .liquid refrigerant evaporates in .the presence of inert gas to produce a refrigerating eilect and absorbing means in which refrigerant vapor is absorbed from inert gas .into absorption liquid, at least one of said means comprising a pair of spaced apart .vertically extending end headers,a number of horizontally extending conduits at different levels, each of said conduits having one end connected to one end header and the opposite end connected to the otherend header, means for conducting liquid for said one means to the uppermost conduit for gravity flow therein, and a connection including a liquid trap for conducting liquid from each conduit to the next lower conduit for gravity flow therein, the circulation of gas through said conduits in a number of parallel flow paths from one end header to the other end header being effected solely due to the varying partial pressure of refrigerant vapor in different parts of the inert gas circuit.

3. In absorption refrigeration apparatus, low and higher temperature places of evaporation in which liquid refrigerant evaporates in the presence of an inert gas to produce a refrigerating effect, first and second places of absorption in which refrigerant vapor is absorbed from inert gas into absorption liquid, connections to provide a primary circuit-for circulation of inert gas which includes said low temperature place of evaporation and first place of absorption, such circulation of inert gas being produced by a driving force developed within the apparatus which is primarily dependent upon the difference inspecific weight of Weak inert gas and enriched inert gas respectively flowing into and from said low temperature place of evaporation, at least one of the places of evaporation and absorption in said primary gas circuit comprising structure providing several paths for flowing inert gas therethrough in parallel, and additional connections to provide another circuit for circulation of inertgas through said higher temperature place of evaporation which includes separate conduit means for conducting enriched inert gas from the latter to said second place of absorption, said first place of absorption being connected to receive inert gas from the second place of absorption only after refrigerant vapor initially is absorbed from inert gas into absorption liquid in the latter.

4. In absorption refrigeration apparatus, low and higher temperature places of evaporation in which liquid refrigerant evaporates in the presence of an inert gas to produce a refrigerating-effect, first and second places of absorption in which refrigerant vapor is absorbed from inert gas into absorption liquid,.connections to provide a primary circuit for circulation of inert gas which includes said low temperature place of evaporation and first place of absorption, such circulation of inert gas being produced by a driving forcedeveloped within the apparatus which is primarily dependent upon the difference in specific weight of weak inert gas and enriched inert gas respectively flowing into .and from said low temperature place of evaporation, at least one of the places of evaporation andabsorption in said primary gas circuit comprising structure providing several paths for flowing inert gas therethrough in parallel, said higher temperature place of evaporation being connected 'to receive at least partially enriched inert gas from said low temperature place of evaporation, and separate conduit means for conducting enriched inert gas from the higher temperature place of evaporation to said second place of absorption, said first place of absorption being connected to receive inert gas fromthe second place of absorp tion only after refrigerant vapor initially is absorbed from inert gas into absorption liquid in the latter.

5. Apparatus as set-forth in claim 4 including means for conducting liquid refrigerant to said higher temperature place of evaporation and from the latter to said low temperature place of evaporation.

6. In absorption refrigeration apparatus, low and higher temperature places of evaporation in which liquid refrigerant evaporates in the presence of an inert gas to produce a refrigerating effect, first and-second places of absorption in which refrigerant vapor is absorbed from inert gas into absorption liquid, connections to provide a primary circuit for circulation of inert gas which includes said low temperature place of evaporation and first place of absorption, such circulation of inert gas being produced by a driving force developed within the apparatus which is dependent upon the diner- 'ence in specific weight of weak inert gas and enriched inert gas respectively flowing into and from said low temperature place of evaporation, said connections including first conduit means for conducting weak :inert gas from said first place of absorption to said low temperature place of evaporation and second conduit means for conducting enriched inert gas from the latter to said first place of absorption, and additional connections to provide another circuit for circulation of inert gas through said higher temperature place of evaporation which includes third conduit means for conducting enriched inert gas from the latter to said second place of absorption, said first place of absorption being connected to receive inert gas from the second place of absorption only after refrigerant vapor initially is absorbed from inert gas into absorption liquid in the latter, and said first, second and third conduit means being formed and arranged so that weak inert gas from the first place of absorption flows in heat exchange relation consecutively with enriched inert gas from one place of evaporation and thereafter with enriched inert gas from another place of evaporation.

7. Apparatus as set forth in claim 6 including means for conducting absorption solution in heat exchange relation with weak inert gas issuing from said first place of absorption and thereafter to said first place of absorption.

8. Apparatus as set forth in claim 6 in which said first, second and third conduit means are formed and arranged so that weak inert gas from the first place of absorption flows in heat exchange relation consecutively with enriched inert gas from said higher temperature place of evaporation and thereafter with enriched inert gas from said low temperature place of evaporation, and means for conducting absorption solution in heat exchange relation with weak inert gas in the part of said first conduit means in heat exchange with said third conduit means and thereafter to said first place of absorption.

9. Apparatus as set forth in claim 8 in which said means for conducting absorption solution is constructed and arranged to bring the solution in intimate contact with weak inert gas in said first conduit means.

SIGURD MATTIAS BACKSTROM.

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